I think I'm having the EXACT same problem, it was such a weird nose, i didnt even know if i could describe it, a propeller plane is ppppperfect, check out the "similar threads" at the bottom I read over some last night and one mentioned a bad bearing on its ways out. And i HAVE been driving with my ABS/Traction control off light on for some time now, I bet the bad bearing that set it off in the first place is just getting worse and now making that sound.

Hope this helps